Add addChainErrorHandler method.

[inamiy]

Psudocode

machine.addRoute(nil=>nil) // connect all states
machine.addRouteChain(1=>2=>3) { ctx in println("SUCCEEDED") }
machine.addChainErrorHandler(1=>2=>3) { ctx in println("FAILED") }

// current state = 0
machine <- 1 // start chaining
machine <- 3 // chaining failed (println FAILED)
machine <- 2 // already failed (no println)
machine <- 1 // reset & start chaining again
machine <- 2 // succeeding...
machine <- 3 // chaining succeeded (println SUCCEEDED)